Flexible plastic electronics, such as Organic Light Emitting Displays (OLEDs) are widely seen as the next generation display technology that will come to replace existing display technology.
One commonly known problem with OLED structures and other oxygen and/or moisture sensitive devices is that they degrade rapidly under atmospheric conditions. In order to protect them from degradation, various types of barrier films have been used to isolate the electroluminescent devices from the environment. It is estimated that for an OLED to achieve reliable performance with a lifetime exceeding 10,000 hours, the encapsulation around the reactive electroluminescent material of the OLED should have an oxygen transmission rate (OTR) less than about 5 to 10 cc/m2/day and a water vapor transmission rate (WVTR) of less than about 10−5 g/m2/day at 39° C. and 95% RH. An ideal bather film for a moist sensitive electronics combines the gas bather properties, chemical resistance and surface properties of glass, with the flexibility, toughness and processability of polymers.
However, commonly used polymer based barrier films which are used to isolate such sensitive structures from the atmosphere have their drawbacks. In general, polymer films 110 do not typically show high bather performance even if they are coated with a metal oxide coating 106 to improve their barrier properties, as they suffer from imperfections such as pinholes 103, cracks 102, gaps occurring at grain boundaries 101 etc. (see FIG. 4)
Integrity of the deposited coatings, such as metal oxide or metal nitride layers is a crucial factor in determining overall gas bather performance, and control of defects, such as pinholes, cracks and grain boundaries within the oxide or nitride layers is a critical requirement. When thickness of the bather film crosses its critical thickness during barrier film growth, cracks formation is observed as a result of intrinsic stresses. Barrier properties of thickness optimized barrier film, having typical thickness range of 30-60 nm, are limited by large pore size defects. The size of pinholes can be further reduced if the coating thickness is increased, but the intrinsic stress would be the limiting factor for the improvement of barrier properties because the intrinsic stress increases as thicker the oxide layer becomes (see FIG. 9).
Current multilayer barrier film technologies require a high quality single barrier oxide layer with less defects, lower stress, and excellent packing density. Conventional methods of fabricating barrier layers for barrier film application, including chemical vapor deposition, physical evaporation methods like electron beam evaporation and Filtered Cathodic Vacuum Arc (FCVA), result in inferior microstructure features, such as pinholes, which are detrimental to gas permeation barriers. This, in turn, affects the quality of multilayer barrier films, as they are built up from the single barrier films.
It is therefore an object of the present invention to overcome at least some of the above mentioned problems.